engleski

Purification of the wastewater from boat pressure washing by electrocoagulation/ozonation

This paper presents the development of the optimum conditions (for the laboratory, pilot and full plant scale) of the removal of heavy metals and organic contaminants from the wastewaters generated by boat pressure washing using the ozonation/electrocoagulation method. The wastewater was collected in the Kastela marina, Kastel Gomilica, Croatia. The initial effluent was highly enriched in heavy metals with elevated levels of organic contaminants. The concentrations of V, Cr, Fe, Cu, Zn, TOC, and COD exceeded the upper permissible limits of 22, 20, 6, 112, 17, 4, and 2 times, respectively. The main mechanisms of the organic matter destruction were the ozone oxidation and the indirect oxidation with chlorine/hypochlorite formed by the anodic oxidation of chloride already present in the wastewater. The removal of heavy metals was forced by the coagulation/flocculation using Fe2+, Fe3+, and Al3+ ions released into the treated solution by electrochemical corrosion of the sacrificial iron and aluminum electrodes. At the optimum conditions obtained with the pilot plant, the removal efficiencies of the parameters V, Cr, Fe, Ni, Cu, Zn, Pb, TOC, and COD were 100.00%, 99.09%, 99.04%, 90.30%, 99.82%, 99.63%, 100.00%, 91.54%, and 84.65%, respectively. All the parameters in the final effluent were in agreement with regulated values. The advantages of this system compared to the physico-chemical treatment are as follows: (1) no need for the external addition of flocculating agents since they are electrochemically generated inside the treatment tank ; (2) minimal pH changes during the treatment process not requiring pH adjustment by acids/basis ; (3) a significantly lower amount of sludge since only Fe and Al ions were released in the solution ; (4) flocs formed by the electrocoagulation can be easily separated by the filtration due to their higher stability, lower content of the bound water and larger surface compared to chemical flocs ; (5) the final EC effluent is clear, colorless and odorless, containing the less total dissolved solids and organics, thence more suitable for the reuse compared to the one obtained by the standard chemical treatment.

electrocoagulation ; ozonation ; antifouling paints

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